An investigation has been made of the coprocessing of paper and other lignocellulosic wastes, and also of waste plastics, with coal via the COsteam route-treatment with CO, water and alkali at elevated pressures. The liquefaction of lignocellulosic and polymeric wastes was studied separately and then with the addition of coal. High conversion of lignocellulosic wastes could be achieved at 400 degrees C. Polypropylene and polystyrene are completely converted to liquids and gases at 400 degrees C; however, the conversion of high density polyethylene requires a temperature of 445 degrees C. Coprocessing of Wyodak coal and lignocellulosics at 400 degrees C did not change the yields or product quality compared with the liquefaction of Wyodak coal or lignocellulosics alone. However, the coprocessing of Wyodak coal and polypropylene at 400 degrees C resulted in a decrease in coat conversion accompanied by an increase in the asphaltene fraction from coal. It is possible that the combination of free radicals from the polymer with coal fragments is responsible for this result. However, coliquefaction of Wyodak coal with less than 30% high density polyethylene at 445 degrees C resulted in good coal conversion (85-90%) and did not increase the asphaltene yield from coal.